This project is concerned with the study of mechanisms by which selective innervation patterns of retinal ganglion cell axons with cells in the optic tectum occur during normal development and following regeneration of the optic nerve in lower vertebrates. Using embryological procedures, the work will evaluate the time course of the development of tectal cells, their innervation by optic axons and final synaptic stabilization leading to the adult pattern. Methods employed will inlude light microscopy, electron microscopy, Golgi analysis, autoradiography and HRP anterograde axonal transport. These experiments will be performed in embryonic and adult goldfish, channel catfish, Xenopus and Rana pipiens. The proposed experiments will determine the formation of retinotopic order within the developing and adult optic nerve. Using morphometric analysis on EM sections, the proposed experiments will seek the mechanisms for expansion of the visual fields following half retinal ablation in goldfish. In addition, experiments are proposed to determine, utilizing tracer methods, the development of optic projections in the albino channel catfish -- specifically the anomalous ipsilateral retinal projection. The role of pigment in the development of normal retinal projections will be studied following heterotopic eye transplantation. The proposed studies will provide detailed information and evidence for cellular interactions during the formation of selective neuronal connections in the visual system of lower vertebrates.